Postfix works on loopback address, but relay access denied on remote connections

I'm making good progress getting ISPConfig 3 and its associated services up and running, but having a persistent issue with a domain configured through ISPConfig. Luros.eu has a catchall address, [email protected] with a forward to my gmail account. When I test through telnet to port 25 locally (on the server), the message gets queued and sent to my gmail. However, when I try to telnet to port 25 from my home machine on a DSL connection or through a webmail interface on a different system (tried Me.com and Hotmail), I get relay access denied.